I've had my iPhone since the day it came out and battery hasn't been a huge concern. Very recently, I noticed it's dying very quickly. It must have gone down about 40% overnight, and then I realized my standby and usage time are the same. I didn't leave anything unusual on overnight either. I tried closing ALL things in multitasking, yet usage still increased when standby increased. Restarting the phone "fixed" the problem. I started to use it again and checked my usage vs standby later: 15 hours 2 minutes vs 15 hours 6 minutes. The problem is back, and again I didn't use or open anything unusual. What could my problem be? FYI, my phone is jailbroken. EDIT Also, I'm running iOS4. No updates.